Conventional air conditioner compressors in hybrid electric vehicles (HEVs) may include insulated gate bipolar transistors (IGBTs) which are three-terminal power semiconductor devices that switch electric power among electrical components. The IGBTs may be cooled inside the compressor by flowing a suction gas over a heat sink area or by operation of a cooling plate in the compressor.
Under some circumstances (such as when the fan motor of the a/c unit is not working optimally, for example), the head pressure of refrigerant leaving the compressor may rise and the IGBTs in the compressor may have a tendency to overheat. The existing compressor controls may be set to terminate operation of the compressor at a predetermined operating head pressure limit (such as 400 psia, for example) under the assumption that the operating temperature of the IGBTs may be excessively high at that pressure. However, in many situations, the operating temperature of the IGBTs in the compressor may actually be within the acceptable temperature range even though the measured head pressure may be equal to or greater than the operating head pressure limit at which operation of the compressor is terminated. Thus, the operating head pressure limit at which operation of the compressor is terminated may be lower than the hardware head pressure limit; therefore, terminating operation of the compressor at the operating head pressure limit may result in premature shutdown of the vehicle air conditioner in many cases.
Accordingly, a compressor control method which prolongs operation of a vehicle air conditioner compressor while preventing overheating of Insulated Gate Bipolar Transistors (IGBTs) in the compressor is needed.